The two essential day trips are inland.
Dorrigo National Park, an hour west, is part of the Gondwana Rainforests of Australia UNESCO listing and the most accessible piece of subtropical rainforest in the country. The Skywalk lookout on the rim of the Dorrigo plateau extends out over the canopy and gives the same view that George Caley saw in 1819. From the visitor centre, the Wonga Walk is a 6 km loop through the rainforest that passes the Crystal Shower Falls (you can walk behind the falling water) and the larger Tristania Falls.
The Waterfall Way is the drive itself — the road from Coffs west through Bellingen, Dorrigo, Ebor and Wollomombi to Armidale, with marked stops at Dangar Falls, Ebor Falls and the spectacular Wollomombi Gorge, the second-highest waterfall in Australia. Allow a full day; stop for lunch in the Heritage-listed town of Bellingen.
The third option, for whale-watching: a half-day cruise from the Coffs Harbour marina in June or September is the best chance to see humpbacks close at hand on their annual migration.